The present invention relates to foam generating nozzles and foam generating systems utilizing the same, and which, while having application for the dispensing of a wide variety of chemicals, has its most important application in the dispensing of cleaning chemicals.
The application of chemicals in a foamed condition is frequently desirable for a number of reasons. Thus, it permits the application of chemicals with lower spray rates and active chemical content with the advantage of reduced costs. Also, especially when spraying vertical or downwardly facing horizontal surfaces, maximum contact time of the foamed material on the surface involved is achieved. Additionally, it eliminates the health and safety hazards caused frequently by liquid sprays which by splashing or otherwise forms tiny droplets or a fine mist which is inhaled and strikes the eyes to cause great discomfort and sometimes serious harm to the persons involved. The application of the material in a foamed state reduces or eliminates the tiny droplets or mist formation which causes these health and safety hazards.
The application of agricultural chemicals by spraying from airplanes and the like by foam generating equipment including a nozzle unit which mixes air with the liquid chemical is well known. Occasionally, cleaning chemicals have been applied by foam-producing aerosol and other type dispensing units. Also, the foaming of a mixture of water and a foaming agent issuing from a nozzle is in common use by firemen.
Many materials such as soaps can be readily foamed by mild agitation, and other materials are more difficult to apply in the foamed condition. Foaming agents can sometimes be added to the latter materials to increase their foamability when agitated by passage through an aerosol nozzle or when mixed with air in an aerating nozzle.
The type of foam achieved by a particular foam generating nozzle unit is a function of a number of factors, such as the nature of the material being sprayed, the pressure of the material when applied to the nozzle unit and the design of the nozzle unit. Also, the desired consistency of the foam to be developed by a particular nozzle unit depends upon the particular application involved. Thus, for applications involving a prolonged desired retention on vertical and downwardly facing horizontal surfaces, it is usually desirable to apply the material involved as a thick foam. Also, it has been discovered that the penetrating power of a material applied to a porous surface is often maximized by applying the material in a foamed condition with minimum sized foam bubbles, which is generally characteristic of a thick foam. In many applications, a thin foam is desired. It is advantageous, therefore, that a given foam generating nozzle unit be readily adjustable to provide a selection of degrees of foaming action with a given chemical and so that the nozzle unit can provide an optimum desired foam with chemicals having different foaming properties and under varying pressure conditions.
Foam generating nozzle units heretofore developed have been less than completely satisfactory for a number of reasons, including their size, complexity and high cost, and/or their inability to be readily adjustable significantly to vary the degree of foaming action achieved thereby or to provide an optimum foam with a wide variety of foamable chemicals, and inlet pressures.
Some examples of foam generating nozzle units heretofore developed are shown in the following patents:
U.s. pat. No. 3,701,482 PA1 U.s. pat. No. 3,446,485 PA1 U.s. pat. No. 2,766,026 PA1 U.s. pat. No. 2,556,239 PA1 U.s. pat. No. 3,094,171 PA1 U.s. pat. No. 3,547,200 PA1 British Pat. No. 627,285
One form of foam generating nozzle unit heretofore developed and which is disclosed in U.S. Pat. No. 3,701,482 includes at the inlet end thereof one or more small orifices through which unaerated liquid passes at a relatively high velocity into the relatively large inlet chamber of a venturi unit having a gradually converging portion communicating with a venturi-forming throat which communicates with an expansion chamber at the outlet end of the nozzle unit. Air ports are located just beyond the high velocity nozzle, through which ports air is sucked by the low pressure developed in the venturi-forming throat. The design of this nozzle unit is such that significant foaming action occurs in only the expansion chamber. The rate of foaming was thought to be a function mainly of the relative size of the throat of the nozzle unit and the total area of the high velocity orifices. The change in foaming action, therefore, required a change in the size of the orifices which did not lend such units to a practical progressive adjustment of the degree of foaming action obtained.
U.S. Pat. No. 3,547,200 to Hout discloses a foam-producing attachment for fog nozzles of the character employed by firemen, in which attachment a variable angle spray pattern issuing from the fog nozzle initially strikes and passes through a conical screen. The flow of the material through the screen causes air to be drawn through the attachment. The velocity of the liquid stream and the air causes a rapid expansion of the foamed stream passing through the screen. The characteristics of the foam stream issuing from the conical screen including the throw of the foam stream are stated to be varied with the angle of the stream issuing from the fog nozzle. In an experiment performed on a commercial form of the device shown in this patent, upon removal of the conical screen, the foam thickness greatly dissipated and the resulting modest character of the foam was about the same as that produced by the fog nozzle separated from the attachment, and the thickness of the foam did not vary significantly with the angle of the stream issuing from the fog nozzle.
The commercial form of this device is a large and unwieldy device being approximately 13/4 feet in diameter and 31/2 feet long and uses a mesh size for conical screen which is unsuitable for use in hand sprayers. Thus, if the size of all parts of the device were to be proportionately reduced to be attachable to hand operated trigger sprayers, the mesh size would be so small as to be incapable of operating on the same principle as the sprayer of the patent, where the liquid stream passes through the same.
British Pat. No. 627,285 discloses a non-adjustable foam producing device wherein a diverging stream is caused to strike the wide end of a modestly tapering passageway where air is drawn into the stream causing the foaming thereof. The stream passes through a long cylindrical passageway forming an extension of the narrow end of the tapered passageway.